It'd be easier if you link me to the mod you're trying to install, then I can explain to you step by step what you have to do to make them work.
You probably either have .img files or .wtd/.wdd files in the package. If it's the first you just go to the location those .img files are located and select import (in SparkIV) to select the corresponding files. If it's wtd/wdd files you open up those images and then select import.
But as I said, link me to the mod you're trying to install and I'll explain it to you in detail